Cook the potatoes and mash them. Add a bit of butter, 2 Tbsp grated cheese, milk, salt, pepper and nutmeg and mix until you get a soft cream, but do not overwork it. When still warm, add the crescenza cheese inside and mix well until melt. Cut the rocket leaves and add them to the potatoes. Cook the pasta in salted water, drain al dente and mix to the potatoes. Lightly butter a oven proof dish, pour the pasta and sprinkle with some more grated cheese. Bake or grill until you get a fine golden crust on top.